A Sound Booster or the Active sound design is an acoustic technology idea that is used in automobiles to change or improve the sound inside and outside the car. To generate a synthetic vehicle sound, active sound design (ASD) frequently employs active noise control and acoustic enhancement techniques.
ASD is used in a variety of ways, from amplifying or diminishing an existing sound to producing a completely new sound. Because there is no single unifying paradigm for ASD, each car manufacturer may employ different software or hardware solutions. Acura’s Active Sound Control, Kia’s Active Sound System, Volkswagen’s Soundaktor, and QNX’s Acoustic Management System are all examples of ASD.
The Lotus Bluebird, which debuted in 1992, was the first vehicle to have active noise cancellation (ANC). Lotus teamed up with Harman International in 2009 to develop a better ANC system that removed noise from the road, tires, and vehicle chassis. Engine systems have become more efficient but less audibly appealing to consumers as a result of the recent need for more frugal and cleaner combustion engine automobiles. Electric and fuel cell vehicles emit high-pitched tones rather than the familiar sound of a combustion engine. Both combustion and electric car makers hope to improve their vehicles’ reception by improving the quality of the interior and exterior vehicle sound with ASD.
Active noise cancellation (ANC) is a software method that eliminates unwanted noise in a vehicle’s interior using existing in-vehicle infotainment gear. Harmonic order reduction is an elimination technique in which undesirable audio signals are detected by sensors and filtered out of the total interior car sound. Manufacturers may utilize adaptive cruise control (ANC) within a vehicle to reduce the impacts of ASD.
Engine sound enhancement (ESE) is a technology that allows manufacturers to augment engine sounds with synthetic noise created from real-time engine data, such as RPM and torque. This artificially created sound is broadcast through the vehicle’s interior or outside speakers. Manufacturers can utilize ESE in ASD to improve perceived engine power without having to make the mechanical changes that other techniques may necessitate.
Smaller engine subsystems have made interior vehicle noise less pleasant in combustion engine vehicles as a result of environmental limitations and a drive for fuel economy in the automotive industry. Electric and hybrid vehicles don’t have a recognizable engine sound, instead opting for a softer high-frequency hum that annoys passengers and puts pedestrians in danger if they don’t detect an approaching vehicle. Consumer desire for a more appealing interior sound, as well as an identifiable brand identity in both the interior and outside of the car that mitigates safety hazards, has risen as a result of these advances.
Sound management in cars used to entail time-consuming mechanical modifications like balance shafts and sound-deadening material, which increased manufacturing time and expense. Manufacturing expenses and problems are decreased with the revival of sound design in the form of ASD. Rather than integrating the technology into the engine structure, the sound can be corrected and tuned for the vehicle at a later stage of development.
To vary the interior and outside noise of the car, active sound design (ASD) uses inputs such as engine and vehicle speed, pedal input, exhaust noise, and vehicle vibrations. To get the required outcomes, these input variables are filtered. ASD variants choose one or more of these factors to create a new sound. These are some of the variations:
- Signals received directly from the engine output and reflected in the vehicle’s interior are referred to as passive sound creation.
- Passive and active sound generation: enhancing the vehicle’s outside noise by amplifying the exhaust input and creating a new output.
- Active mounts: take vibration inputs from the outside vehicle and transmit vibration outputs to the inside of the vehicle.
- Synthetic sound is the process of creating a new sound using the internal stereo audio system.
Theory and Application
Cylinders are responsible for burning gasoline and providing energy to power the vehicle in a standard combustion engine. These cylinders fire on a regular basis, and their output can be reduced to a series of sinusoidal waves (by conventions of the Fourier transform). The engine crankshaft’s rotations per minute (RPM) and the firing order, or layout, of the cylinders determine the shape of these sine waves. Digital signal processing (DSP) techniques can be used to enhance engine sound in the passenger cabin by amplifying harmonic orders of engine sound that are lacking from the interior sound.
The engine load situation is determined by acceleration sensors on older vehicles’ engines, or by the Controller Area Network bus (CAN-bus) in current cars, to collect the missing orders. The missing orders are relayed using dynamic band-pass filters (a device that relays specific frequencies). The signal is routed through cascading high- and low-pass filters to reduce artefacts (disruptive clicks) during the transfer. The orders are amplified through the car firewall (body separating the engine from the inside) and interior sound system using an adaption of the engine’s RPM signal (recorded by an inductive voltage transformer).
Subharmonics and Sound Signatures
Virtual (synthetic) noises are frequently utilized in electric and fuel cell vehicles to compensate for the lack of a combustion engine sound. Manufacturers must acknowledge the psychoacoustic theories behind sound preference in order to build the best sound design in an electric vehicle (EV). Experimental investigation compared a subjective rating of sound quality components with J.D. Power’s APEAL study in a study of diesel engine sound quality.
Manufacturers attempt to lessen loudness increment and high-frequency sound for a more pleasant driving experience based on customer preference surveys in vehicle interiors. The standard car noise is muffled in current EVs by an RPM-dependent low-pass-filtered sound. This low-pass-filtered sound is a synthetic sound with a lower frequency that is dependent on the EV’s actual engine parameters, such as speed and load.
This virtual noise is subjected to Alt and Jochum’s simple-integer ratio harmonic order approach. The original high-frequency components of the EV are then separated from subharmonics (lower-frequency copies).  Individuals subjectively regarded these subharmonics as preferred for the interior sound of an EV in an evaluation of many generated sound stimuli. 
Vehicles with internal combustion engines react dynamically to changing driving conditions. Manufacturers must consider a sound identity that includes a dynamic driving sound when creating a brand sound for an electric vehicle. A base sound signature is made up of sub-signatures and micro-signatures that can be enlarged to improve the sound’s dynamic quality. These sub-signatures can be linked to factors (such as load and speed) or maneuvers that send specific sound samples. The sound produced by creating micro-signatures in EV drivetrains is more vibrant and expressive than the EV’s basic frequencies.
Consumer Response to Challenges
The emergence of ASD is mostly ignored by the general consumer. Consumers, on the other hand, are dissatisfied with the synthetic engine sound in contemporary BMW vehicles. Numerous instructional videos and articles about disabling the ASD in BMW vehicles can be found online, as well as articles about the false-sounding synthetic noise.
For electric and fuel cell automobiles, a brand identity was created.
Typical combustion engine automobiles emit auditory feedback that conveys the car’s brand identity while in operation. The frequency of sound fluctuates minimally throughout a period of acceleration in electric and fuel cell vehicles due to the single gear system and layout of power converters, and is not well suited to the actual state of the vehicle speed and load. Additionally, the lack of engine noise creates a spectral gap (empty space) between wind and road noise, amplifying individual vehicle components and lowering cabin sound quality.
Manufacturers must choose between recreating a normal combustion engine sound or generating a totally new sound idea to build a brand identity.
The combustion engine process is re-created.
The micro structural fluctuations (variations between cylinder firings) of the combustion process may not be accurately reproduced by current active sound design implementations in combustion engine cars. Identifying and recreating the harmonic engine instructions is inefficient since the signal waves emanate from several regularly firing cylinders. Furthermore, this method presupposes that the combustion engine is uniform. Because the force generated by the cylinders is periodic and may vary from one cycle to the next, it is impossible to duplicate the natural component of engine noise.
ASD technology is used by several automakers in their own branded versions.
- By filtering through the auditory data it receives, an engine management system in vehicles like the BMW M5 improves the noises supplied by speed and engine power. Drivers can change the interior acoustics as well as the vehicle’s performance by selecting a driving mode.
- Similarly, the Kia Stinger has five drive modes (environment, comfort, smart, sport, and custom) that change the volume and aggression of the sound inside the vehicle. This car is designed to react to human preferences and is equipped with a turbocharged engine. The turbocharger improves efficiency by forcing more compressed air into the combustion engine, resulting in a more constant and clear sound.
- A Helmholtz resonator and a sound symposer are used in Porsche’s ASD implementation to transfer engine noises directly into the car cabin. The Helmholtz universal resonator reduces engine noise by using an electronically controlled valve that oscillates with air, similar to the sound made when blowing over a bottle’s top. The sound symposer is made up of a line of plastic tubing with a membrane and flap valve that functions similarly to the human ear. The resonator and sound symposer open fully when the Sport button is pressed, amplifying the engine sound in the car cabin.